1. Field of the Invention
The present invention relates generally to semiconductor wafer processing, and more particularly, to a method and apparatus for cleaning substrate edges before, during and after fabrication operations.
2. Description of the Related Art
In the semiconductor chip fabrication process, it is well known that there is a need to clean the surface of the substrate (e.g., wafer) of unwanted residues to maximize the yield of defect-free chips. Unwanted residues are sometimes left behind during fabrication operations. Examples of fabrication operations include plasma etching, material depositions, and chemical mechanical planarization (CMP). CMP is a typical polishing technology and is performed on both dielectric and conductive materials.
During the plasma etching process, the surface of the wafer exposed to the plasma is etched. The etching produces byproducts due to the physical and chemical reactions of the etch gases and the materials being etched. The byproducts can adhere to the wafer edge, bevel and underside where the ion bombardment is minimal. In the deposition process, metals are commonly deposited over previously formed dielectric features such as interconnect trenches and vias. During this deposition, it is possible that excess metal material is inadvertently deposited on the edge of the wafer. During the CMP process, chemical slurries such as silica-based slurry, dispersed silica, fumed or dispersed alumina are used to facilitate the removal of oxides and metals. Residues from the CMP process are also likely to adhere to the edges of the wafer, even after some later cleaning steps. The residue materials and particles noted above will tend to orient themselves on unprotected portions of the wafer and condense along the edge, notch, edge exclusion regions and the underside of the wafer. These residues tend to harden over the fabrication cycles and will result in what is referred to as “bevel polymer”, due to their structure and chemical composition. Bevel polymers have unique properties, in that they adhere to each other and to the wafer surface with a strong bond, and the bond is relatively hard to break. If the bevel polymer is not removed during wafer processing, the bevel polymer may flake off and can deposit on surfaces of other wafers during wafer transport and storage. Further, the flakes can cause defects, such as scratches on the wafer surfaces, inappropriate interactions between metallization features, etc. These defects have the downside of causing yield loss.
Several well-known techniques have been suggested and implemented to address the issue of cleaning the wafer edges with varying degrees of success. Brush scrubbing and edge scrubbing techniques have been used. However, these techniques use soft materials (e.g., polyvinyl alcohol ‘PVA’) that are designed to prevent scratching of the wafer surface. Thus, these soft materials are not capable of breaking the strong bond of the bevel polymers deposited on the wafer edges.
In view of the foregoing, there is a need for an apparatus and method for enhancing wafer edge cleaning.